This research will: (1) establish a system to monitor HIV risk behavior among IDUs not in treatment in selected District of Columbia neighborhoods, 2) evaluate an intervention model to prevent the spread of HIV among IDUs, crack users, and their sexual partners, and 3) examine the interaction of individual and network factors in predicting program participation and risk behavior change. Subjects recruited from target census tracts with high composite HIV risk scores will be interviewed regarding their risk behavior for HIV, and asked to participate in a study of social networks. All subjects will be provided pre-HIV test counseling, offered an HIV test, and provided post-test HIV counseling approximately one week later. Following the initial interview, subjects will be randomly assigned to monitoring only, standard, or enhanced intervention. All subjects in standard and enhanced interventions will be reinterviewed at 6 and 12 months followup. The analytic framework will be a quasi-experimental, repeated measures design examining changes in risk behavior within the two intervention groups, with the monitoring only group for comparison. The major outcome variables are changes in drug use risk, sexual risk, and knowledge and attitudes about AIDS. The Risk Behavior Assessment (RBA) instrument will be used at study entry, and the Risk Behavior Followup Assessment (RBFA) at 6 and 12 months followup. A substudy will test the hypothesis that individuals with low self efficacy will reduce less in dense and hierarchical networks than those in less dense and less hierarchical networks. Risk reduction among individuals with high self-efficacy will be unrelated to network structure.